1. Field of the Invention
The present invention relates to an electronic device, e.g. a mobile phone, having a lightguide plate used in a planar light source that illuminates a liquid crystal display panel and operation keys of the electronic device.
2. Description of the Related Arts
Liquid crystal display apparatus for image display are widely used in displays of mobile phones, personal digital assistants (PDAs), mobile personal computers (PCs), automatic teller machines (ATMs), etc. These liquid crystal display apparatus employ a backlight unit that applies illuminating light to a liquid crystal display panel from the back thereof to enhance the luminance of the display screen. The backlight unit uses a lightguide plate that guides light from a light source, e.g. a fluorescent lamp or light-emitting diode (LED) light source, and that emits the light toward the liquid crystal display panel from the entire area of a light exiting surface thereof. In the meantime, electronic devices such as mobile phones use operation keys and employ a light source that illuminates the operation keys from the back thereof, for example, to facilitate operations performed in dark.
Regarding such electronic devices, Japanese Patent Application Publication No. 2001-358816, for example, proposes a lighting device for an electronic device that uses a single sheet-shaped lightguide plate comprising a first lighting part that illuminates a liquid crystal panel, and a second lighting part that illuminates a key operation part having a plurality of operation keys. Japanese Patent Application Publication No. 2002-49439 proposes a foldable electronic device that has a lightguide plate for a liquid crystal panel and a lightguide plate for a key operation part separately from each other. The lightguide plate for the liquid crystal panel receives light from an LED or other light source through one end edge surface thereof and emits a part of the light from the other end edge surface thereof. The lightguide plate for the key operation part receives the part of the light emitted from the lightguide plate for the liquid crystal panel and uses the light to illuminate the key operation part.